Researchers demonstrate new way to ‘squeeze’ infrared light

Researchers have shown for the first time that a specific class of oxide membranes can limit or ‘squeeze’ infrared light – a finding that holds promise for the next generation of infrared imaging technologies. The thin-film membranes retain infrared light much better than bulk crystals, the established technology for trapping infrared light.

“The thin-film membranes maintain the desired infrared frequency but compress the wavelengths, allowing imaging devices to capture images with greater resolution,” said Yin Liu, co-corresponding author of a paper on the work and assistant professor of materials science and engineering at North Carolina State University.

‘We have shown that we can limit infrared light to 10% of the wavelength, while maintaining its frequency. This means that the time it takes for a wavelength to change is the same, but the distance between the peaks of the wave is the same. much closer together. Bulk crystal techniques limit infrared light to about 97% of the wavelength.”

“This behavior was previously only theoretical, but we were able to demonstrate it experimentally for the first time through both the way we prepared the thin-film membranes and our novel use of synchrotron near-field spectroscopy,” said Ruijuan Xu, co-lead author of the paper and assistant professor of materials science and engineering at NC State.

For this work, the researchers worked with transition metal perovskite materials. Specifically, the researchers used pulsed laser deposition to grow a 100-nanometer-thick crystalline membrane of strontium titanate (SrTiO).₃) in a vacuum chamber. The crystalline structure of this thin film is of high quality, meaning it has very few defects. These thin films were then removed from the substrate on which they were grown and placed on the silicon oxide surface of a silicon substrate.

The researchers then used technology from Lawrence Berkeley National Laboratory’s Advanced Light Source to perform synchrotron near-field spectroscopy on the strontium titanate thin film while it was exposed to infrared light. This allowed the researchers to capture the material’s interaction with infrared light at the nanoscale.

To understand what the researchers have learned, we need to talk about phonons, photons and polaritons. Phonons and photons are both ways that energy travels through and between materials. Phonons are essentially the energy waves caused by the way atoms vibrate. Photons are essentially waves of electromagnetic energy.

You can think of phonons as units of sound energy, while photons are units of light energy. Phonon polaritons are quasiparticles that form when an infrared photon is coupled to an ‘optical’ phonon, meaning a phonon can emit or absorb light.

“Theoretical papers proposed the idea that transition metal perovskite oxide membranes would allow phonon polaritons to confine infrared light,” says Liu. “And our work now shows that the phonon polaritons trap the photons and also keep the photons from extending beyond the surface of the material.

“This work creates a new class of optical materials for controlling light in infrared wavelengths, which has potential applications in photonics, sensors and thermal management,” says Liu. “Imagine being able to design computer chips that can use these materials to release heat by converting it into infrared light.”

“The work is also exciting because the technique we have demonstrated for making these materials means that the thin films can be easily integrated with a wide variety of substrates,” says Xu. “That should make it easy to incorporate the materials into many different types of devices.”

The paper, “Very Limited Epsilon-Near-Zero and Surface-Phonon Polaritons in SrTiO₃ Membranes,” is published in the journal Nature communication.